1. Field of the Invention
The invention relates to personal computers having CMOS memory for storing basic system configuration parameters, and more particularly to battery powered personal computers which do not have a separate battery to power the CMOS memory.
2. Description of the Prior Art
When International Business Machines Corp. (IBM) introduced the PC/AT, its second major generation of personal computers, one of the components in the computer was a small CMOS memory/real-time-clock (RTC) unit. This component was used to provide time keeping functions and to provide storage of configuration parameters, such as the type of floppy disk drive, the amount of memory, and so on when the computer was turned off, so that when the computer was next turned on, the configuration information was readily available to ease initialization in startup of the system and the time was accurate so that user entry was not required. The CMOS memory/RTC unit was powered by a separate battery which powered only that unit when the computer was turned off. When the computer was turned on, the main power supply provided the power. Because of the separate battery, power could be maintained to the CMOS memory/RTC unit even while the computer was turned off. This allowed the storage and time keeping to continue.
As personal computers developed, variations included portable and, ultimately, laptop and notebook computers. These computers generally contain the functions of the desktop systems. For example, they include hard drives, large amounts of memory and many additional options and new features. These additional functions required the storage of additional configuration information, so that the original CMOS memory area was quickly filled up and an extended CMOS memory area was utilized. The goal of portable computers was always reduced size and weight, to allow improved portability. Thus space and weight are at a premium, as well as cost. Therefore there is always a desire to eliminate components to save space, weight and cost.
One major characteristic of the portable computers was that when they reached laptop and notebook size they were usually battery powered. This allowed them to be operated remotely and greatly increased their flexibility. However, battery life was often relatively short, so that frequent charging was needed or the computer would become unusable. In addition, the batteries were almost always removable, allowing multiple battery packs to be utilized if an extended duration was required away from a power source. While this use of multiple battery packs extended the operating time, the need to change batteries always seemed to occur in the middle of program operation, so it was desirable to keep the computer in its operating state, or at least in some operating state wherein the program and data memory was not lost, while the batteries were changed. To this end small auxiliary batteries were placed in the notebook computers so that they could power the system for a very short time, often at reduced power levels, while the main battery was replaced. When the new main battery was installed, the computer was brought back to full operation and the user could continue activities.
During this evolution, the battery for the CMOS memory/RTC unit remained in the computer. But this CMOS battery added expense and weight and took up space and at first blush would be considered not necessary, as there were already two other batteries in the computer anyway. It would appear straightforward to simply remove the CMOS battery and allow the other two batteries to power the CMOS memory/RTC portion. The problem with this was that, as noted above, the main battery is often removed for replacement. In such a case, the auxiliary battery might very well be in a discharged state. Alternatively, both batteries might be discharged after an extended period of non-use. In either case, then all data in the CMOS memory/RTC unit would be lost. The user would then have to completely go through setup and configuration of the computer system as if it were newly obtained. This would be quite troublesome for numerous reasons. First, in the battery removal case it would occur as yet an additional problem when the basic program being executed had just been lost because of the low battery problems. Second, it is a time consuming process as the number of configuration items has grown quite large. Third, the actual user in many cases does not know the settings in the computer. The computer would have been set up by a knowledgeable individual and given to the user in a configured mode. The user will have no idea of what most of the items are, so frustration will increase. To avoid these problems, it was previously considered necessary to retain the additional battery for the CMOS memory/RTC unit, even though it took up precious space inside the laptop computers and added to the cost and weight. Therefore it would be desirable to develop some technique wherein this CMOS battery could be removed and yet abate the concern about potential loss of configuration information should the main battery be removed and the auxiliary battery be discharged.